JP2507839B2 - Stirrer - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stirrer, and in particular,
The present invention relates to a stirrer for efficiently performing stir processing such as liquid mixing, dissolution, crystallization, reaction, and slurry suspension under stirring operation conditions from a turbulent flow region to a laminar flow region.

[0002]

2. Description of the Related Art As is well known, various types of stirring blades are used in stirring devices according to the purpose thereof.
There are turbine-type blades for low-viscosity blades and double-helical blades for high-viscosity blades, but with a relatively simple blade configuration, stirring mixing of low-viscosity liquid to high-viscosity liquid, that is, layering from turbulent flow regions As a means for achieving agitation and mixing under a wide range of agitation operation conditions up to the basin, a multi-stage agitation blade configuration in which two-blade type paddle blades are provided in a combination of upper and lower two stages or three or more stages is often adopted.

In a stirring device having such a multi-stage stirring blade structure, from the viewpoint of the rotational balance of the blades and the mechanical strength of the rotating shaft against the fluid pressure fluctuations acting on the blade surface, each blade is
Overwhelmingly adopted is the method of crossing each other at a 90-degree crossing angle, and generally, from the viewpoint of power consumption, the height of the blades is made small and the distance between each blade is greatly increased. They are arranged in multiple stages in the open state.

[0004]

On the other hand, in recent years, the demands on the performance of stirring devices have become more sophisticated and diversified, and there is a demand for a stirring device capable of supporting a wider range of stirring conditions. Particularly in the batch process, a stirring device that satisfies various and high-level stirring and mixing conditions as described below is desired. Uniform mixing: Good mixing in a wide viscosity range and good uniform mixing corresponding to changes in liquid amount and viscosity can be achieved. Heat transfer mixing: Good heat transfer ability is obtained at low power stirring. Solid-liquid agitation: A wide range of solid-liquid agitation such as dispersion of particles having a relatively high sedimentation rate, uniform mixing of high-concentration slurry and uniform mixing at low shear (low rotation) can be achieved.

Liquid-Liquid Dispersion: A sharp liquid droplet size distribution can be obtained, and a liquid-liquid dispersion that achieves both low shear and light liquid dispersion in a liquid whose viscosity increases with stirring can be achieved. Simple wing shape; each wing shape is simple and can be applied to glass-lined reactors.

In order to meet these demands, the inventors of the present invention have studied various conventional stirring devices having a multi-stage stirring blade structure. As a result, it is not so difficult to select a stirrer that individually satisfies each of the above conditions, but it is very difficult to select specifications that simultaneously satisfy many items. It turns out that something needs to be improved or developed.

In the above conventional stirring device in which the crossing angle of each paddle blade is 90 degrees, the flow patterns formed around each blade due to the flow of the fluid discharged from each blade are not sufficiently connected. Therefore, the fluid becomes a factor of separating into upper and lower layers in the stirring tank, and also causes a dead space in the tank, which adversely affects the mixing performance. In addition, the generation of dead space not only causes the heat transfer performance of the fluid to deteriorate, but also tends to cause sticking and contamination on the inner wall surface of the tank, thus lowering the stirring efficiency.

Further, when flat blade type stirring blades such as paddle blades are arranged in multiple stages in the vertical direction, a plurality of independent circulation flows are formed around each blade in the stirring tank due to the rotation of each blade. Then, this tendency becomes more noticeable when the blade-to-blade distance L between the upper blade (61) and the lower blade (62) is widened, as shown in (a) of FIG. In this case, the circulating flows of the two blades interfere with each other to form a boundary B of the flow, and the boundary B suppresses the mixing of the upper and lower fluids. On the contrary, to prevent the interference of the circulation flows between the blades (b)
As shown in the figure, it is conceivable to reduce the inter-blade distance L by moving one of the wings, but in this case,
In order to secure the total blade height, the height of the blade plate of one of the blades is increased by the amount by which the distance L between the blades is reduced (h 'in the figure).
It becomes necessary to increase the consumption power. Also,
In this case, the circulation flow is divided at the center of the blade whose height of the vane plate is enlarged, and a flow boundary B ′ is generated due to the interference of the circulation flows as seen when the blades are widened. As a result, it may be a factor that disturbs the connection of the entire flow in the stirring tank.

However, in order to solve these problems, the optimum crossing angle of each blade and the distance between the blades are determined from the viewpoint of the flow pattern of the entire stirring tank formed by the flow of the fluid discharged from each blade. No theoretical or quantitative disclosure has been known so far, which makes it difficult to select specifications to meet recent demands.

The present invention is intended to solve the above-mentioned problems, and has a stirring blade structure in which upper and lower multi-stage paddle blades are arranged in an optimum positional relationship for mixing, and an appropriate pressure gradient is provided between the paddle blades. An agitation that forms a connection of the resulting flow, and this flow forms one large circulation flow that extends over the entire agitation tank to improve the agitation efficiency of the liquid under agitation operation conditions from the turbulent flow region to the transition flow and the laminar flow region. The purpose is to provide a device.

[0011]

In order to achieve the above object, the present invention provides, as a first invention, a stirring device characterized by having the following constitutions. That is, the stirring device of the first invention is a stirring device having a vertical cylindrical stirring tank and a rotating shaft vertically provided at the center of the stirring tank. A plurality of paddle blades are mounted vertically and in multiple stages with respect to the rotation axis, and the blade plates of each paddle blade are mounted as axially symmetrical as possible, and the height of the blade plates is ½ or more of the blade diameter. The bottom paddle blade having at least two blades held vertically and having a blade diameter of 1/2 or more of the inner diameter of the stirring tank is arranged close to the bottom surface of the stirring tank. Between the paddle blade and the paddle blade, there is a space in which a baffle can be interposed, and the blade diameter of the upper blade of each vertically adjacent paddle blade is equal to or smaller than the blade diameter of the lower blade. The distance between the upper and lower paddle blades that are adjacent to each other is 20% or less of the inner diameter of the stirring tank. The upper blade of each paddle blade is mounted so as to precede the lower blade in the rotational direction at an intersection angle of 45 to 75 degrees.

A second invention is a stirring device characterized by having the following constitutions. That is, the stirring device of the second invention is a stirring device having a vertical cylindrical stirring tank and a rotating shaft vertically provided at the center of the stirring tank, and is composed of two blade plates held vertically. A plurality of paddle blades are mounted vertically and in multiple stages with respect to the rotation axis, and the blade plates of the paddle blades are mounted axially symmetrically, and the height of the blade plates is 1/2 or more of the blade diameter. It is possible to arrange a lowermost paddle blade having a blade diameter of 1/2 or more of the inner diameter of the tank close to the bottom surface of the stirring tank, and to insert a baffle plate between the inner surface of the stirring tank and the paddle blade. The upper stage blade diameter of the vertically adjacent paddle blades is equal to or smaller than the lower stage blade diameter, and the distance between the vertically adjacent paddle blades is the inner diameter of the stirring tank. 20% or less of the upper-stage blades of adjacent paddle blades vertically adjacent to each other, and the upper-stage blades intersect with the lower-stage blades at an angle of 45 to 75 degrees. It is mounted so as to precede the direction of rotation by the difference angle.

It is characterized in that

In addition, in the above first or second invention, a third invention is a stirring device characterized in that the outer end portion of the paddle blade at the lowermost stage is formed as a retreating blade.

In the above first, second or third invention, at least a pair of paddle blades of the vertically adjacent paddle blades partially overlap each other in the vertical direction at their outer ends. A stirrer characterized by the above is a fourth invention.

A fifth aspect of the present invention is a stirrer characterized by having the following constitutions. That is, the stirring device of the fifth invention is a stirring device having a vertical cylindrical stirring tank and a rotating shaft vertically provided at the center of the stirring tank, and is composed of two blade plates held vertically. Two-stage or three-stage paddle blades are mounted vertically with respect to the rotation axis and the blade plates of each paddle blade are mounted axially symmetrically, and the height of the blade plates is 1/2 or more of the blade diameter. Yes, the outer end of the lowermost paddle blade having a blade diameter of 1/2 or more of the inner diameter of the stirring tank is formed as a receding blade, and the lowermost paddle blade is arranged close to the bottom surface of the stirring tank. There is a space in which a baffle plate can be interposed between the inner surface of the stirring tank and the paddle blade, and the blade diameter of the upper blade of each vertically adjacent paddle blade is the same as the blade diameter of the lower blade. The distance between the paddle blades that are equal to or smaller than each other and are vertically adjacent to each other is 20% or less of the inner diameter of the stirring tank. At least a pair of paddle blades of the paddle blades partially overlap with each other in the vertical direction at the outer end portions, and the upper blades of the vertically adjacent paddle blades have an angle of 45 to 75 degrees with respect to the lower blades. It is characterized in that it is mounted so as to precede the direction of rotation at the intersecting angle.

A sixth aspect of the present invention is a stirrer having the following constructions. That is, the stirring device of the sixth invention is a stirring device having a vertical cylindrical stirring tank and a rotating shaft vertically provided at the center of the stirring tank, and is composed of two blade plates held vertically. At least a pair of paddle blades are vertically and multi-staged with respect to the rotary shaft, and the blade plates of the paddle blades are mounted axially symmetrically, and the paddle blades at the lowest stage having a blade diameter of 1/2 or more of the inner diameter of the stirring tank are stirred. It is arranged close to the bottom of the tank, and there is a space between the stirring tank inner surface and the paddle blade where a baffle plate can be interposed. The lower blades are mounted at a crossing angle of 45 to 75 degrees so as to precede in the rotational direction, and the height of the blades is ½ or more of the blade diameter. The distance between the blades is characterized by being 20% or less of the inner diameter of the stirring tank.

Further, a seventh invention is a stirring device according to the sixth invention, characterized in that the outer end of the lowermost paddle blade is formed as a retreat blade.

Further, in the sixth or seventh invention, the stirring device is characterized in that the diameter of the upper blade of the vertically adjacent paddle blades is smaller than that of the lower blade. And

Further, in the sixth, seventh or eighth invention, at least a pair of paddle blades of vertically adjacent paddle blades partially overlap each other in the vertical direction at least at one position of the outer end portion. A ninth aspect of the present invention is a stirrer characterized in that.

A tenth aspect of the present invention is a stirrer having the following features. That is, the stirring device of the tenth invention is a stirring device having a vertical cylindrical stirring tank and a rotating shaft vertically provided at the center of the stirring tank. The stirring device is composed of two blade plates held vertically. Two-stage or three-stage paddle blades are mounted vertically with respect to the rotation axis and the blade plates of each paddle blade are mounted axially symmetrically, and the height of the blade plates is 1/2 or more of the blade diameter. Yes, the outer end of the lowermost paddle blade having a blade diameter of 1/2 or more of the inner diameter of the stirring tank is formed as a receding blade, and the lowermost paddle blade is arranged close to the bottom surface of the stirring tank. There is a space in which a baffle plate can be interposed between the inner surface of the stirring tank and the paddle blade, and the blade diameter of the upper blade of each vertically adjacent paddle blade is smaller than the blade diameter of the lower blade. The distance between the upper and lower paddle blades that are adjacent to each other is 20% or less of the inner diameter of the stirring tank. At least a pair of paddle blades partially overlap each other at the outer end in the vertical direction, and the upper blades of the vertically adjacent paddle blades have an intersection angle of 30 degrees or more and less than 90 degrees with respect to the lower blades. It is mounted so as to precede the direction of rotation. It is characterized by:

The eleventh invention is an agitator in the first, second, fifth, sixth or tenth invention, wherein each blade is substantially a flat plate.

[0023]

The fluid in the stirring tank is discharged in the radial direction by the rotation of the stirring blade. In a stirrer in which the paddle blades are arranged in upper and lower stages, the fluid is discharged from each paddle blade, so the smooth connection of the flow from the paddle blades without interfering with each other improves the mixing efficiency. Will be an important point.

When the fluid is agitated by the rotation of the upper and lower multi-stage paddle blades, a discharge flow in the radial direction is formed around each blade as shown in FIG. 6 (a). At the same time, a circulation flow is formed that splits in the vertical direction and heads again toward the center of each blade. The discharge flow formed by these blades interferes with the discharge flow of the other adjacent blade to separate the fluid into upper and lower layers, and affects the discharge flow of the other blade in the radial direction. As a result, it becomes a factor that disturbs the flow connection in the entire stirring tank.

Furthermore, when the crossing angle of each blade is 90 degrees which is commonly used in the prior art, it is advantageous in terms of mechanical strength, but depending on the viscosity range, the flow between the upper and lower blades should be smoothly connected. Becomes difficult and becomes a factor that disturbs the flow connection in the entire stirring tank.

Therefore, the present inventors first of all, in the arrangement relationship in which the inter-blade distance is small and the discharge flows formed by the upper and lower blades are easily connected to each other, the movement of the circulating flow formed by each blade and the crossing angle are As a result of detailed examination of the relationship, these circulation flows affect the other blade with a certain rotation delay phase, and the correlation between the rotation delay phase and the crossing angle indicates the formation of the circulation flow in the tank. It was found that it greatly affects

That is, when the crossing angle of the upper and lower paddle blades is changed, the vertical positional relationship between the pressure rising portion generated on the front surface and the pressure dropping portion generated on the rear surface of these paddle blades also changes according to the crossing angle. Therefore, when selecting a crossing angle within a certain range, it was found that the connection of discharge flows from the upper and lower paddle blades is most stable.

As a result of studying these relationships in more detail, when the discharge flow formed by one paddle blade flows to the high pressure side in front of the other paddle blade, the discharge flows interfere with each other and the entire stirring tank is affected. It becomes difficult to form a circulating flow that extends over. On the contrary, when it flows to the low pressure side of the rear surface of the other paddle blade, a selective flow from the high pressure side to the low pressure side is formed between the upper and lower blades without disturbing each other's discharge flow. It was concluded that the discharged streams could be well connected, which resulted in one large circulation flow throughout the stirred tank due to the optimum pressure gradient, which could enhance the stirring efficiency of the fluid.

It is also inferred that the upper paddle blade should precede the lower paddle blade by less than 90 degrees in order to generate the optimum flow pattern for mixing due to such a pressure gradient. Reached

In order to confirm this inference, the inventors selected a stirrer in which the paddle blades are arranged so as to intersect with each other in upper and lower two stages as a model of the basic form, and based on this model stirrer, the upper stage blades are The lower blade crossing angle α (the leading angle of the upper blade relative to the rotation direction of the upper blade), the blade-to-blade distance L between the upper blade and the lower blade, and the lower blade shape that affects the discharge force balance between the upper blade and the lower blade ( The effects of the swept wing and the straight paddle wing) were investigated by numerical and mixed experiments.

Numerical experiments consist of numerical analysis of flow and simulation of mixing using the analysis results. First, the three-dimensional flow velocity distribution in the stirring tank was obtained, and then the results were used to obtain the time-dependent change in the concentration distribution of the diffusing substance charged from the liquid surface by simulation. In addition, the application of this numerical experiment,
It was limited to the laminar watershed where the numerical results of fluid analysis are highly reliable. On the other hand, in the mixing experiment, inner diameter 400 mm, height 800 mm, capacity 80 Lt
And, two kinds of large and small stirring tanks having an inner diameter of 200 mm, a height of 400 mm, and a capacity of 10 Lt were used, and for the measurement of the mixing time, a decolorization method of reducing and decolorizing the color of iodine starch with sodium thiosulfate was used. The iodine solution and the sodium thiosulfate solution were prepared to have the same viscosity as the stirring liquid, and the mixing time was determined from the continuous photographs of the decolorization process.

First, the influence of the difference in the crossing angle α between the upper blade and the lower blade on the flow and mixing process in the stirring tank was evaluated by a numerical experimental method. In this experiment, a paddle blade with a blade diameter d 120 mm (0.6 D) was placed in a stirring tank with an inner diameter D 200 mm, and the distance L between the blades was L.
20mm (0.1D) is arranged in two stages, the viscosity μ 5Pa ・ s, the density ρ1400kg / m ³ , the stirring Reynolds number Re 8.4, the stirring liquid, the liquid depth H 200mm (1.0D), the rotation speed of the blade 2.08r. Under the common condition of / s, the crossing angle α of the upper and lower blades was changed from 0 degree (the upper and lower blades were arranged in the same plane) to 90 degrees and the stirring was performed. A typical example of the flow velocity distribution and mixing process in the experiment is shown in FIG. This [Fig. 7] is a diagram showing the flow velocity vector and the concentration contour line showing the mixing progress of the diffusive substance in the 1/2 vertical section of the stirring tank. (A) Fig. 7 shows an example in which the intersection angle α is 45 degrees. ,
(b) The figures show examples where the crossing angle α is zero degrees.

When the crossing angle α is set to zero, the fluids discharged from the upper paddle blade and the lower paddle blade collide with each other between the blades as shown in FIG. Inhibits liquid transport. On the other hand, when the crossing angle α is 45 degrees, the liquid is actively transported from the upper part to the lower part of the stirring tank as shown in FIG.

The difference in the mixing process corresponding to this is as follows.
When the crossing angle α is 0 degree, the diffusive material is not transported to the lower blade even if 30 seconds have passed after the injection, whereas the crossing angle α is 45
In some cases, the diffused material is transported to the bottom of the tank 30 seconds after the addition.
That is, rather than arranging the upper and lower paddle wings on the same plane,
By arranging these blades at an intersection angle of 45 degrees, the flows of the upper blade and the lower blade are connected, and rapid mixing is achieved. In addition, as a result of examining various intersection angles α using this method,
The intersection angle α is in the range of 30 degrees or more and less than 90 degrees, preferably 45 degrees.
From 75 to 75 degrees was found as an appropriate angle range, and it was confirmed that the above-mentioned reasoning holds.

Subsequently, in order to grasp the optimum range of the blade-to-blade distance L between the upper blade and the lower blade, the upper-to-lower crossing angle α is set to 45 degrees, while the blade-to-blade distance L is set to the inner diameter D of the stirring tank. 10% of
From 30 to 30%, and an experiment was conducted by stirring under the same conditions as above. The flow velocity distribution from the experiment is shown in FIG. It should be noted that [Fig. 8] is a diagram showing the flow velocity vector in the 1/2 vertical section of the stirring tank.
An example of setting D (10%) is shown in (b).
An example in which (20%) is set is shown in (c).
Examples are set to 0%).

As the inter-blade distance L increases from 0.1D to 0.3D, as shown in [FIG. 8], the degree of the discharge flow of the upper paddle blade entering the rotational range of the lower paddle blade decreases. , 0.3D, it was pushed back to the discharge flow of the lower paddle blade with almost no entry. On the other hand, below 0.2D, the flow enters into the rotation range of the lower paddle blade and is connected. Therefore, the distance L between the blades is 0.2 D or less, preferably 0.1
By setting to D, the flow in the stirring tank is connected, and efficient mixing can be realized.

Furthermore, the discharge force balance between the upper stage blade and the lower stage blade is important for efficient stirring and mixing with the multistage blade configuration. In this experiment, the discharge force balance in the laminar flow region and the turbulent flow region was examined. As the lowest paddle blade, a retreating blade whose outer end was formed as a retreating blade was adopted to enhance the discharge force in the lower part of the agitating tank and to improve the viscosity compatibility and power efficiency. Three
FIG. 9 shows an example of the radial discharge velocity analysis results around the normal linear paddle blade and the retreating blade blade in the laminar flow for the single blade type. It is to be noted that FIG. 9 (a) is a diagram showing the radial discharge flow velocity distribution around the backward blade, and FIG. 9 (b) is a diagram showing the radial discharge flow velocity distribution around the linear paddle blade.

As shown in [FIG. 9],
There is no liquid suction S at the rear surface of the blade tip, which is observed in a straight paddle blade, and the liquid is discharged over a wide angle range, and the maximum discharge flow velocity is 30 times that of a straight paddle blade with the same outer diameter. %large.

On the other hand, since the discharge flow velocity of the paddle blade depends on the outer diameter (blade span) of the paddle blade, in order to enhance the discharge force in the lower part of the stirring tank, the paddle blade in the lowermost stage may be placed in another position above it. A larger diameter than the paddle wing can also be used.

According to the optimum conditions grasped above, if a multi-stage paddle blade with a crossing angle α of 45 degrees and an inter-blade distance L of 0.1 D is used, in the laminar flow area with a viscosity of 2 Pa · s or more, the entire stirring tank is Was mixed well. However, in the state of transition from laminar flow with viscosity less than 2 Pa · s to turbulent flow, the flow connection between the upper and lower blades became unstable, and mixing tended to be slightly delayed.

As a result of various studies to solve this problem, when the upper and lower adjacent paddle blades are vertically overlapped with each other at least at the outer end portions thereof, the flows discharged from the paddle blades are adjacent to each other. The paddle wing can be connected to the rotation range of the paddle wing.
As a result, it was concluded that the flow pattern due to the optimum pressure gradient is formed, and that the stirring efficiency can be increased even for the fluid in the transition region.

In order to confirm the effect, strip-shaped fins are provided at both outer lower end portions of the upper paddle blade so as to project downward and overlap the lower paddle blade.
With this configuration, a stirring liquid having a viscosity of 2 Pa · s or less was stirred under the above conditions.

As a result, the fin portions provided on both outer lower ends of the upper stage paddle blades made stable the flow connection of the upper and lower stage paddle blades and realized the rapid mixing. Further, by providing the fin portion, not only good uniform mixing can be obtained in the transition region and the turbulent flow region, but also better mixing can be performed in the laminar flow region as compared with the case without the fin portion. Was confirmed.

The present invention has been made on the basis of the various conditions confirmed in the above-mentioned investigation. That is,
Arranging the upper paddle blades of the multiple paddle blades mounted on the rotary shaft in multiple stages in the vertical direction with respect to the adjacent lower paddle blades in the rotation direction at an intersection angle of less than 90 degrees. Then, the flow of the upper blade and the lower blade is connected to realize rapid mixing. In addition, the intersection angle is 45 degrees to 75
By adjusting the degree, the flow connection between the upper blade and the lower blade becomes more stable, and more reliable and rapid mixing is realized.
In addition, by forming the outer end of the paddle blade at the lowest stage into a retreating blade, the discharge force in the lower part of the stirring tank is strengthened, the flow pattern inside the stirring tank is stabilized, and the viscosity compatibility and power efficiency are improved. Improve. Also, by making the bottom paddle blade larger in diameter than the other paddle blades located above it, the discharge force in the lower part of the stirring tank is strengthened and the flow pattern of the entire stirring tank in the turbulent region is stabilized. In addition, the viscosity compatibility and power efficiency are improved.

By setting the distance between the upper and lower adjacent paddle blades to be 20% or less of the inner diameter of the stirring tank, the flow connection between the upper blade and the lower blade is made more stable, and Achieves efficient mixing. Also, by overlapping vertically adjacent paddle blades with each other at least at the outer end portion in the vertical direction, the fluid in the transition region can be surely and stably connected to the flow of the upper stage blade and the lower stage blade. Achieves uniform mixing.

[0046]

Embodiments of the present invention will be described below with reference to the drawings. [FIG. 1] is a drawing showing an agitator of one embodiment of the present invention, in which (a) is a perspective view with a part cut away, (b)
The figure is a cross-sectional view taken along the line BB of FIG. The present embodiment is an example in which the stirring blade structure of the present invention is applied to a glass lining type device.

In FIG. 1, (1) is a stirring tank, and this stirring tank (1) has a jacket (1) for heat exchange on the outer periphery.
It is formed into a vertical cylindrical container equipped with a). Further, two baffle plates (6) are hung from the upper part of the stirring tank (1) at an equal pitch in the circumferential direction near the inner peripheral surface.

Reference numeral (2) is a rotary shaft, and the rotary shaft (2) is vertically installed at the center of the stirring tank (1), and is installed in the upper central portion of the stirring tank (1). ), It is rotationally driven in the direction shown by arrow A in FIG.

The lower blade (3) is composed of two blades (3a) and (3b) held vertically, and these blades (3a) (3b)
Is axisymmetric, and the height h ₁ of the blade is 1/2 of the blade diameter d ₁ .
The blade diameter d ₁ is 1 / the inner diameter D of the stirring tank.
2 or more. The lower blade (3) has a lower edge formed along the curved surface of the bottom of the agitation tank (1), and both outer sides formed as retreating blades with respect to the rotation direction indicated by arrow A in (b). The paddle type blade, which is installed on the lower end of the rotating shaft (2),
It is placed close to the bottom of (1).

The upper blade (4) is composed of two blade plates (4a) (4b) held vertically, and these blade plates (4a) (4b)
Is axisymmetric, and the height h ₂ of the blade is 1/2 of the blade diameter d ₂ .
It is the above size. This upper blade (4) has a blade diameter d ₂
Is a paddle-shaped blade having substantially the same diameter as the blade diameter d ₁ of the lower blade and provided with strip-shaped fins (4f) protruding downward at both outer lower ends thereof. It is mounted on the upper rotary shaft (2). Further, the upper blade (4) sets the intersection angle α shown in (b), that is, the intersection angle preceding the lower blade (3) in the rotation direction indicated by the arrow A to 45 degrees, and The lower edges of the outer fins (4f) are located lower than the upper edges of both outer sides of the lower blade (3) by a predetermined dimension Δh, and are arranged vertically overlapping the lower blade (3). . Further, the upper blade (4) and the lower blade (3) are mounted on the rotating shaft (2) so that the distance between the blades is 20% or less of the inner diameter of the stirring tank.

In order to confirm the effect of improving the mixing efficiency in the medium and high viscosity regions of the stirrer having the above-mentioned structure, "the blade diameter of the upper blade is equal to that of the lower blade, and the upper and lower paddle blades have the same diameter. The size of the stirring tank is 1/2 or more the inner diameter, and the height of the upper and lower paddle blades is 1/2 or more of the blade diameter.
The blade distance between the upper blade and the lower blade is 20% or less of the inner diameter of the stirring tank,
In comparison with a stirring device in which the crossing angle between the upper blade and the lower blade is 90 degrees, which is conventionally used, the stirring Reynolds number Re
In the laminar flow condition of 11.7, the velocity vector distribution and the concentration curve of the diffusive substance at the liquid surface and the tank bottom were obtained by numerical experiments. In this experiment, a blade diameter d 120mm (0.6D) was set in a stirring tank with an inner diameter D 200mm.
The paddle blades of No. 2 were arranged in two stages, the crossing angle α was 45 degrees, the liquid depth H was 250 mm (1.25 D), and the number of rotations of the blades was 2.08 r / s. Further, the overlap dimension Δh with respect to the lower blade of the upper blade fin portion of the apparatus of this embodiment was set to 0.05D. The results are shown in [Fig. 2]. [FIG. 2] is a diagram showing a flow velocity vector and a concentration response curve in the stirring tank, and FIG. 2 (a) is according to the present embodiment,
As a comparative example, FIG. (b) shows a stirring device in which the crossing angle α is 90 ° which is a conventionally used angle.

The intersection angle α is 90, which is a conventionally used angle.
As shown in Fig. (B), although there is a connection between the upper and lower paddle blades in the stirrer with a certain degree, there is a slight difference in the concentration between the liquid surface and the bottom of the tank even after about 180 seconds. Mixing is not over. On the other hand, in the stirring device of this embodiment,
(a) As shown in the figure, the upper and lower blades flow well,
After about 90 seconds, the concentrations of the liquid surface part and the bottom part of the tank were the same, and the mixing was completed.

As described above, the stirring device of the present embodiment can achieve stirring and mixing in a significantly short time, which is less than half of the mixing time by the stirring device in which the intersecting angle α is 90 ° which is a conventionally used angle. Was confirmed. Further, both the upper and lower blades have a simple shape, and when the glass is coated on the outer surface integrally with the rotary shaft, there is little problem of deformation caused by high temperature firing, and the glass lining type equipment as in this example Easy to apply.

In the stirring device of the example shown in FIG. 1, the upper and lower stirring blades are constituted, but this is an example. For example, as shown in FIG. 3, paddle type blades are used. May be arranged in three stages above and below, and a stirring blade configuration of three or more stages may be adopted according to the scale of the apparatus and the liquid depth without departing from the gist of the present invention. . Further, only the uppermost blade of the multi-stage paddle blade may be made of one blade plate. Also, two baffle plates (6) were arranged near the inner peripheral surface of the stirring tank. The baffle plate (6) converts the swirling flow into an upward flow, forming a circulation flow over the entire stirring tank. Therefore, good mixing can be achieved. However, this baffle plate is not always necessary for stirring and mixing the high-viscosity liquid. The point is that there should be a space in which a baffle can be interposed between the inner surface of the stirring tank and the paddle blades.

FIG. 3 is a perspective view in which a part of a stirring device according to another embodiment of the present invention is cut away, and those designated by the same reference numerals as in FIG. 1 are equivalent, The description is omitted here.

In the stirring device of this embodiment, the upper blade (4) is provided with the fins (4f) at both outer lower ends on the rotary shaft (2) above the lower blade (3) as in FIG. ) Is installed in two stages, upper and lower, and has a total of three stages of stirring blades. Also,
The lower blades (3) and the upper blades (4) of the second stage are arranged with their mutual intersecting angle set to 45 degrees, and the upper blades (4) of the second stage
Are arranged such that each fin portion (4f) vertically overlaps the adjacent lower blade.

According to the stirring blade structure as in this embodiment,
It is possible to uniformly stir the entire area of the tank according to changes in the liquid depth, and it is possible to easily cope with an increase in the size of the apparatus and an increase in stirring capacity.

In the stirring device of the examples shown in FIGS. 1 and 3, strip-shaped fin portions (4f) are provided at both outer lower ends of the upper blade (4), and the fin portions (4f ) Is vertically overlapped with the other blades located below to stabilize the flow connection between the paddle blades that are vertically adjacent to each other, but this is only an example. As long as it does not deviate from the gist of the present invention in which the paddle blades overlap each other at least at the outer ends in the vertical direction, for example, as shown in FIG.
(3) and the upper blade (4) are provided with strip-shaped fins at one outer end of each, and as shown in (b) of [Fig. 4], both outer lower ends of the upper blade (4). A fin portion projecting like a fish tail is provided in the portion, and furthermore, as shown in FIG. 4 (c), the fish tail is provided at both outer ends of the lower blade (3) and the upper blade (4). It is also possible to provide fin portions projecting in a circular shape and allow them to overlap each other in the vertical direction.

Further, in the stirring device of the examples shown in [FIG. 1] and [FIG. 3], the lowermost blade is retracted in order to enhance the discharge force in the lower part of the stirring tank to improve viscosity correspondence and power efficiency. Although it was formed on the blade blade, this is not necessarily a backward blade blade, and in order to enhance the discharge force at the bottom of the tank, the bottom blade is a paddle-shaped blade with a larger diameter than other blades located above it. You can also deal with

FIG. 5 is a drawing showing a stirring device according to still another embodiment of the present invention, in which (a) is a vertical sectional view and (b) is
It is a BB cross-sectional view of FIG.

In FIG. 5, (11) is a stirring tank, and this stirring tank (11) has a jacket (1) for heat exchange on its outer periphery.
It is formed into a vertical cylindrical container equipped with 1a). Also,
On the inner peripheral surface of the stirring tank (11), four baffle plates (16) are vertically mounted at equal pitches in the circumferential direction toward the center.

(12) is a rotary shaft, and the rotary shaft (12)
Is vertically installed at the center of the stirring tank (11) and is rotationally driven in the direction shown by arrow A in the figure (b) by a drive unit (15) mounted at the upper center of the stirring tank (11). .

(13) is a lower blade, (14) is an upper blade, and these upper and lower blades (14), (13) are paddle type blades having the same blade diameter d and blade plate height h. , These upper wing (14) and lower wing (13)
And the blade-to-blade distance L between them is set to 20% or less of the inner diameter D of the agitation tank (11), which is attached to the rotating shaft (12). Also, lower wing (13)
Has a lower edge formed in a shape along the curved surface of the bottom of the stirring tank (11) and arranged in the vicinity of the bottom surface of the stirring tank (11), while the upper blade (1
In 4), the crossing angle α shown in FIG. 7B, that is, the crossing angle preceding the lower blade (13) in the rotation direction indicated by the arrow A is set to less than 90 degrees.

A specific example of mixing / stirring performed by changing the crossing angle α of the upper and lower blades by the stirrer having the above configuration will be described below.

Under the above structure, the inner diameter D of the stirring tank (11)
200mm, upper and lower blades (14), (13) blade diameter d is 120mm
(0.6D), the height h of the blades is 70mm (0.35D), and the blade-to-blade distance L is 20mm (0.1D = d / 6), while the upper and lower blades (1
4), three kinds of stirring devices having the intersection angle α of (13) set to 45 degrees, 60 degrees and 75 degrees were prepared. For comparison, the stirring device has the same configuration as that of the present embodiment except that the crossing angle α between the upper and lower blades is 90 degrees and the blade distance L is 60 mm (0.3 D), which is conventionally used. I also prepared.

Then, using these four kinds of stirring devices and under the same conditions with the blade rotation speed set to 125 rpm, the viscosity μ = 5 Pa · s,
Liquids having a density ρ = 1400 kg / m ³ were mixed and stirred, and the complete mixing time of each liquid was measured.

As a result, the complete mixing time of the liquid required 150 seconds in the comparative example with the crossing angle of 90 degrees, whereas in the example of this example, the crossing angle was 45 degrees. 1
In the case of 04 seconds and 60 degrees, it is 102 seconds, and in the case of 75 degrees, it is 114 seconds.
It could be significantly increased to 25% to 30%, and the excellent mixing effect of the device of the present invention could be confirmed.

In this embodiment, the blade distance L between the upper and lower blades is set to 20 mm, but this is only an example, and this blade distance L is 20% of the stirring tank inner diameter D (40 mm = d / 3) The following dimensions should be set. The mixing effect due to the blade-to-blade distance can be expected in the case of blades of a predetermined size. That is, in a large paddle blade in which the blade diameter of the lowermost paddle blade is 1/2 or more of the inner diameter of the stirring tank and the height of the blade plate is 1/2 or more of the blade diameter, the distance between the blades is set to the stirring tank. By setting the inner diameter to 20% or less, the upper and lower flows in the tank are connected, and efficient mixing can be realized.

However, for reducing the distance between the blades,
As described in the [Prior Art] section, although there is an increase in power consumption with an increase in the total blade height for dealing with the liquid depth, from the viewpoint of shortening the mixing time, this inter-blade distance is At 20% or less (preferably around 10%), the size and cost of the equipment will be selected.

Further, in this embodiment, the lower blade is a paddle-shaped blade having the same blade diameter and blade plate height as the upper blade, but this is an example, and the lower blade is the same as in the first embodiment. It is also effective to form the retreating blades or to make the lower blades have a larger diameter than the upper blades to strengthen the discharge force at the lower part of the stirring tank and smoothly connect the entire flow in the tank. . Further, in this embodiment, the upper and lower two stages of stirring blades are used for the purpose of facilitating the evaluation and explanation of the effects of the structure of the present invention. It goes without saying that similar mixing / stirring efficiency can be achieved even if a multi-stage stirring blade configuration having two or more stages is adopted according to the scale and the liquid depth.

Further, as described above, in order for the flows of the upper blade and the lower blade to be connected to each other and rapid mixing be achieved, the intersecting angle of the upper blade with respect to the lower blade is 30 degrees or more and 90 degrees or more.
It has been described that the crossing angle is within the range of less than 40 degrees, preferably 45 degrees to 75 degrees. The following can be seen from the results of the "stirring / mixing experiment using the stirrer".

That is, in an agitation-mixing experiment using the agitator having the configuration shown in FIG. 1, the agitator of the present embodiment was arranged so that "the upper blade and the lower blade have substantially the same blade diameter, and the upper and lower paddle blades have the same blade diameter. The size is 1/2 or more of the inner diameter of the tank, and the height of the upper and lower paddle blades is 1/2 or more of the blade diameter.
The distance between the upper blade and the lower blade is 20% or less of the inner diameter of the stirring tank, the outer edge of the lower blade is formed as a retreat blade, and the upper blade and the lower blade partially overlap each other in the vertical direction. Precedes the lower blade in the direction of rotation at a crossing angle of 45 degrees. ]] Has the characteristic. On the other hand, the comparative example in the experiment is that "the blade diameter of the upper blade is equal to that of the lower blade,
The diameter of each lower paddle blade is 1/2 or more of the inner diameter of the stirring tank, and the height of the upper and lower paddle blades is 1 / the blade diameter.
This is a stirring device having a size of 2 or more, a blade distance between the upper blade and the lower blade of 20% or less of the inner diameter of the stirring tank, and an intersecting angle between the upper blade and the lower blade being 90 degrees, which is conventionally used. As a result, the stirring and mixing of the stirring device of the present example is completed in about 90 seconds, but the stirring and mixing of the comparative example does not end even after about 180 seconds. That is, it can be seen that the stirring device of this example having the above characteristics can shorten the stirring and mixing time to about 1/2 or less as compared with the stirring device of the comparative example. That is, the "mixing effect", "retracting blade effect" and "crossing angle effect" reduced the stirring and mixing time to 1/2 or less.

On the other hand, in the stirring and mixing experiment by the stirring device having the configuration of FIG. 5, the stirring device consisting of two upper and lower paddle-shaped blades having the same blade diameter and blade plate height was used. Each example in which the distance between the blades was set to 20% or less (10%) of the inner diameter of the stirring tank, and the upper blade was attached to the lower blade so as to precede the lower blade in the rotational direction at the intersecting angles of 45 °, 60 °, and 75 ° ”. "The blade diameter and the height of the blades are the same as those in this embodiment, the intersecting angle between the upper blade and the lower blade is 90 degrees, and the distance between the upper blade and the lower blade is 30% of the inner diameter of the stirring tank. Comparative Example ”is to compare the stirring and mixing time.

As a result, the intersection angles are 45 degrees, 60 degrees, and 7 degrees.
The stirring and mixing time of each example of 5 degrees was 104, respectively.
Seconds, 102 seconds, 114 seconds. On the contrary, the stirring and mixing time of the comparative example having the intersecting angle of 90 degrees is 150 seconds. That is, according to the stirring device of the present embodiment, the intersecting angle between the upper blade and the lower blade is 45 degrees, and the distance between the upper blade and the lower blade is 20% or less of the inner diameter of the stirring tank. It can be seen that the stirring and mixing time can be shortened to about 2/3 as compared with the stirring device of the comparative example. That is, the stirring / mixing time is 2 / for the “effect of the crossing angle” and the “effect of the distance between the blades”.
It became 3. This means that the stirring / mixing time is 2 /
It is shown that the factor that could be shortened to 3 is other than the intersection angle. That is, the stirring and mixing time cannot be reduced to 2/3 only by the effect of the crossing angle.

The results of the above stirring and mixing experiment can be summarized as follows. That is, "the effect of the receding blade",
By the "overlap effect" and the "crossing angle effect", the stirring and mixing time can be reduced to about 1/2 or less as compared with the stirring apparatus of the comparative example which does not have these characteristics. Further, by the "effect of the distance between blades" and the "effect of the crossing angle", the stirring and mixing time can be shortened to about 2/3 as compared with the stirring device of the comparative example which does not have these characteristics. That is,
It is not possible to reduce the stirring and mixing time to 2/3 only by the "effect of the crossing angle", and the above numerical values "1/2" and "2/3"
When calculated backward, the stirring and mixing time can be shortened to about 3/4 or less as compared with the stirring device which does not have these characteristics due to the "reverse blade effect" and the "overlap effect".

Based on the results of this examination, the crossing angle that causes the upper blade to precede the lower blade in the rotational direction is 45 degrees to 75 degrees.
The stirring device according to claim 10 having the requirements according to claims 1 to 9 except that the angle is not less than 30 degrees and not less than 90 degrees, and the stirring efficiency of the fluid with respect to the stirring device that does not have these requirements is It is clear that this can be improved.

[0077]

As described above, the stirring device according to the present invention has a structure in which upper and lower multi-stage paddle blades are arranged in a clear and optimum positional relationship for mixing, and is suitable for each paddle blade. A flow resulting from the pressure gradient is formed to connect the flow patterns in the entire stirring tank, and the stirring efficiency of the fluid under the stirring operation condition from the turbulent flow region to the laminar flow region can be significantly improved.

[Brief description of drawings]

1A and 1B are views showing a stirring device according to an embodiment of the present invention, in which FIG. 1A is a partially cutaway perspective view, and FIG. 1B is a cross-sectional view taken along line BB in FIG. 1A. Is.

2A and 2B are diagrams showing a flow velocity vector and a concentration response curve in a stirring tank, wherein FIG. 2A shows one example of the present invention, and FIG. 2B shows a comparative example.

FIG. 3 is a perspective view in which a stirring device according to another embodiment of the present invention is partially cut away.

FIG. 4 is a view for explaining an overlapping form of vertically adjacent paddle wings according to the present invention.

5A and 5B are views showing a stirring device according to still another embodiment of the present invention, wherein FIG. 5A is a vertical sectional view, and FIG. 5B is a sectional view taken along line BB of FIG. 5A.
FIG.

FIG. 6 is a schematic diagram for explaining the relationship between the inter-blade distance L and the circulation flow in a stirring device in which paddle blades are arranged in a multi-stage structure. (A) is a diagram when the inter-blade distance L is increased, (b) ) The figure shows the case where the distance L between the blades is reduced.

FIG. 7 is a diagram showing the influence of the crossing angle of the upper and lower blades on the flow velocity vector in the stirring tank and the concentration contour line showing the mixing progress. (A) in FIG. 7 shows that the crossing angle is 45 degrees. b) The figure shows the crossing angle at zero degrees.

FIG. 8 is a diagram showing the influence of the inter-blade distance L on the flow velocity vector in the stirring tank, where (a) is the case where the inter-blade distance L is 10% of the inner diameter of the tank, and (b) is the inter-blade distance. When L is 20% of the inner diameter of the tank, (c) shows the case where the inter-blade distance L is 30% of the inner diameter of the tank.

FIG. 9 (a) is a diagram showing a radial discharge flow velocity distribution around a swirl blade, and FIG. 9 (b) is a diagram showing a radial discharge flow velocity distribution around a linear paddle blade.

[Explanation of symbols]

(1), (11) ... stirring tank (2), (12) ... rotating shaft (3), (13) ... lower blade (4), (14) ... upper blade (5), (15) ... drive device (3a), (3b), (4a), (4b) ... slats (6), (16) ... baffles D ... stirring vessel inner diameter d, d _1, d ₂ ... blade diameter h, h _1, h ₂ … Height of blades α… Angle of intersection L… Distance between wings

Claims (11)

(57) [Claims] 1. A stirrer having a vertical cylindrical stirring tank (1) and a rotating shaft (2) vertically provided at the center of the stirring tank, characterized by having the following constitutions. apparatus. One or more vertically held blades (3a, 3b)
A plurality of paddle blades consisting of the above are installed vertically and in multiple stages with respect to the rotation axis, and the blade plates of each paddle blade are mounted as axially symmetrical as possible, and the height (h ₁ ) of the blade plates is _{1 of the} blade diameter (d ₁ ). / 2 or more in size, having at least two blade plates held vertically, and having a blade diameter (d ₁ ) of 1/2 or more of the inner diameter (D) of the stirring tank at the lowest stage (3) is arranged close to the bottom surface of the stirring tank, and a baffle plate (6) is provided between the inner surface of the stirring tank and the paddle blades.
A space capable of interposed, blade diameter of the upper stage blade of the paddle blades which are adjacent in the vertical (4) (d ₂₎ is equal to the impeller diameter (d ₁₎ of the lower stage blade (3) Or smaller, the inter-blade distance (L) between vertically adjacent paddle blades is 20% or less of the stirring tank inner diameter (D), and the upper blade (4) of vertically adjacent paddle blades is the lower blade. It is mounted so as to precede the blade (3) in the direction of rotation at an intersecting angle (α) of 45 to 75 degrees. 2. A stirrer having a vertical cylindrical stirring tank (1) and a rotating shaft (2) vertically provided at the center of the stirring tank, characterized by having the following constitutions. apparatus. A plurality of paddle blades consisting of two vertically held blade plates (3a, 3b) are mounted vertically and in multiple stages with respect to the rotation axis and the blade plates of each paddle blade are mounted axially symmetrically, and the height of the blade plate is increased. is (h ₁₎ is 1/2 or more of the size of the impeller diameter (d _1), the lowermost paddle blade is 1/2 or more of the blade diameter of the stirring tank inside diameter (D) (d ₁₎ ( 3) is placed close to the bottom surface of the stirring tank, and a baffle plate (6) is placed between the inner surface of the stirring tank and the paddle blades.
A space capable of interposed, blade diameter of the upper stage blade of the paddle blades which are adjacent in the vertical (4) (d ₂₎ is equal to the impeller diameter (d ₁₎ of the lower stage blade (3) Or smaller, the inter-blade distance (L) between vertically adjacent paddle blades is 20% or less of the stirring tank inner diameter (D), and the upper blade (4) of vertically adjacent paddle blades is the lower blade. It is mounted so as to precede the blade (3) in the direction of rotation at an intersecting angle (α) of 45 to 75 degrees. 3. The stirrer according to claim 1, wherein an outer end portion of the lowermost paddle blade (3) is formed as a retreating blade. 4. At least a pair of paddle blades (3, 4) among the vertically adjacent paddle blades partially overlap each other in the vertical direction at the outer end portions thereof. The stirring device according to 2 or 3. 5. A stirrer having a vertical cylindrical stirring tank (1) and a rotating shaft (2) vertically provided at the center of the stirring tank, characterized by having the following constitutions. apparatus. A two-stage or three-stage paddle blade composed of two vertically held blade plates (3a, 3b) is mounted vertically with respect to the rotation axis and the blade plates of each paddle blade are mounted axially symmetrically, the height of the slats (h ₁₎ is 1/2 or more of the size of the impeller diameter (d _1), the bottom is 1/2 or more of the blade diameter of the stirring tank inside diameter (D) (d ₁₎ The outer end of the paddle blade (3) is formed as a retreat blade and the lowermost paddle blade (3) is arranged close to the bottom surface of the stirring tank, and between the inner surface of the stirring tank and the paddle blade. Is a baffle (6)
A space capable of interposed, blade diameter of the upper stage blade of the paddle blades which are adjacent in the vertical (4) (d ₂₎ is equal to the impeller diameter (d ₁₎ of the lower stage blade (3) The distance between adjacent upper and lower paddle blades (L) is 20% or less of the inner diameter (D) of the stirring tank, and at least one pair of upper and lower paddle blades (3, 4) partially overlap each other at the outer end in the vertical direction, and the upper blades (4) of the vertically adjacent paddle blades intersect the lower blade (3) at an angle of intersection of 45 to 75 degrees ( It is mounted so that it precedes in the direction of rotation at α). 6. A stirrer having a vertical cylindrical stirring tank (1) and a rotating shaft (2) suspended from the center of the stirring tank, characterized by having the following constitutions. apparatus. At least a pair of paddle blades consisting of two vertically held blade plates (3a, 3b) are mounted in a multi-stage vertically with respect to the rotation axis, and the blade plates of each paddle blade are mounted axially symmetrically, and the stirring tank inner diameter With a blade diameter (d ₁ ) greater than 1/2 of (D)
A certain lowermost paddle blade (3) is arranged close to the bottom surface of the stirring tank, and a baffle plate (6) is placed between the inner surface of the stirring tank and the paddle blade.
The paddle vanes vertically adjacent to each other have the upper stage vanes (4) rotating at an intersection angle (α) of 45 to 75 degrees with respect to the lower stage vanes (3). The height (h ₁ ) of the vane plate is 1/2 or more of the blade diameter (d ₁ ) and the inter-blade distance (L) between vertically adjacent paddle blades is Is 20% or less of the inner diameter (D) of the stirring tank. 7. The stirrer according to claim 6, wherein an outer end portion of the lowermost paddle blade (3) is formed as a retreating blade. 8. The blade diameter (d ₂ ) of the upper blade (4) of the vertically adjacent paddle blades is smaller than the blade diameter (d ₁ ) of the lower blade (3). Or the stirring device according to 7. 9. At least one pair of paddle blades (3, 4) of the vertically adjacent paddle blades has at least one outer end portion.
The stirring device according to claim 6, 7 or 8, wherein the portions partially overlap each other in the vertical direction. 10. A vertical cylindrical stirring tank (1) and the stirring tank
For a stirring device having a rotating shaft (2) vertically installed in the inner center
Oite, 攪to feature in that it has the following configuration -
Stirrer . From the two vertically held blades (3a, 3b)
2 or 3 stages of paddle blades above the rotation axis
The vanes of each paddle vane are mounted in the downward direction in an axially symmetrical manner , and the height (h ₁ ) of the vanes is 1/2 or more of the vane diameter (d ₁ ).
And the blade diameter (d ₁ ) of 1/2 or more of the inner diameter (D) of the stirring tank
The outer edge of a certain lowermost paddle blade (3) is formed as a retreat blade
And put the bottom paddle blade (3) close to the bottom of the stirring tank.
The baffle plate (6) between the inner surface of the stirring tank and the paddle blades.
The upper stage blades (4) of the paddle blades vertically adjacent to each other having a space capable of interposing
(D ₂ ) is smaller than the blade diameter (d ₁ ) of the lower blade (3) , and the blade distance (L) between adjacent upper and lower paddle blades is agitation.
It is 20% or less of the tank inner diameter (D), and at least one pair of vertically adjacent paddle blades
The paddle wings (3, 4) are vertically aligned with each other at the outer ends.
The upper blades (4) of the paddle blades that partially overlap and are vertically adjacent to each other are
Crossing angle of 30 degrees or more and less than 90 degrees with respect to the step wing (3)
(Α) is mounted so as to precede the rotation direction . 11. Stirrer according to claim 1, 2, 5, 6 or 10, characterized in that each blade (4a, 4b) is substantially a flat plate.